Chemotaxis, or the oriented movement of a cell with reference to a chemical agent is a complex and highly integrated process. The movement may be positive (toward) or negative (away) with respect to the chemical gradient. Once triggered, this process in turn mediates, among many things, tissue organization, organogenesis and homeostasis and ultimately orchestrates embryonic morphogenesis; contributes to tissue repair and regeneration; and drives disease progression in cancer, mental retardation, atherosclerosis, and arthritis. The migrating cell is highly polarized with complex regulatory pathways that spatially and temporally integrate its component processes.
Chemotaxis occurs in both prokaryotes and eukaryotes. In all cases, movement toward an agent or stimulus is termed positive chemotaxis (i.e., the agent or stimulus is chemoattractive for the cell), while movement away from an agent or stimulus is termed negative chemotaxis (i.e., the agent or stimulus is chemorepulsive for the cell). Chemoattraction (CA) and chemorepulsion (CR) are therefore properties of the agent or stimulus, while chemotaxis is a property of cells.
It is believed that for both prokaryotes and eukaryotes, cells undergoing chemotaxis sense a change in agent concentration and, thereby, move along a concentration gradient.
Chemotaxis is known to occur for several types of eukaryotic cells. Within the immune system, chemotaxis is often driven by a class of biological agents, known as chemokines (or chemotactic cytokine).
Chemotaxis, and the related phenomenon, chemokinesis (the enhancement of random cellular movement in response to a chemical or biological agent, irrespective of agent concentration), have been examined in subpopulations of mammalian cells. Chemorepulsion, however, has rarely been described as a physiological phenomenon. In one instance, the chemokine SDF-1 (a.k.a. SDF-1α, CXCL12) has been described as a chemorepellent in the context of a two-dimensional transmigration apparatus and at a concentration 10-fold above that necessary for the induction of chemoattraction in the same device. Observationally, the response allegedly induced by SDF-1, termed “fugetaxis,” appears to be analogous to chemorepulsion, as the latter term is known in the art. However, it is not clear whether “fugetaxis” is truly different from chemorepulsion.
Moreover, chemorepulsion of immune cells in response to non-chemokine biological or chemical agents has never been described.
A thorough understanding of the mechanisms underlying cell migration will facilitate development of therapies for the treatment of cell migration-related disorders.